Allogeneic hematopoietic stem cell transplantation (HSCT) is an important therapy with curative potential for a variety of malignant diseases, including leukemias, lymphomas and some solid tumors. Despite significant progress in reducing treatment-related mortality, malignant relapse remains a major problem. Studies regarding non-myeloablative HSCT and donor leukocyte infusions have irrefutably demonstrated that the donor immune system can generate a graft-versus-tumor (GVT) effect that can prevent or treat malignant relapse. At the same time advances in tumor vaccines have resulted in promising pre-clinical and clinical results. We hypothesize that immunization of HSCT recipients against specific tumor antigens can decrease the risk of relapse without enhancing graft-versus-host disease (GVHD). We propose to use clinically relevant mouse allogeneic HSCT models and DMA vaccines which encode for specific melanoma and lymphoma differentiation antigens. In our preliminary studies with two different DNA vaccines in HSCT recipients we have found specific anti-tumor T cell responses, significant tumor protection and no evidence of GVHD. In Specific Aim 1 we will analyze the efficacy of post-transplant tumor vaccination of HSCT recipients. We will measure T and B cell responses, assess the effects on tumor protection, GVHD and overall survival, and determine the optimal time point after transplant for tumor vaccination. In Specific Aim 2 we will study adjuvant strategies to enhance the efficacy of post-transplant tumor vaccination with DNA vaccines in HSCT recipients, including the administration of IL-7 and IL-15, the co-delivery of DNA encoding for IL-7 and IL-15, and CTLA-4 blockade. In Specific Aim 3 we will study the efficacy of adoptive therapy with donor T cells in combination with DNA vaccines in HSCT recipients. These studies will lead to a better understanding of the mechanisms involved in post-transplant vaccination with melanoma and lymphoma differentiation antigens, and could result in the development of novel therapeutic strategies by combining allogeneic HSCT, post-transplant tumor vaccination and adoptive T cell therapy.